In acoustic container processing systems, an object or sample is held within a gas-filled chamber, at a location away from the walls of the chamber by an acoustic standing wave field. It is often desirable to maintain the object at its equilibrium levitation position without substantial oscillations of the object about that position. In the prior art, it was found that when a sample was displaced from its equilibrium position, as when it was initially placed in the acoustic field, the sample would oscillate about its equilibrium position. It would often require tens of minutes for viscous drag from the gas in the chamber to damp the oscillations and cause the sample to lie completely stable. There are also applications where it is desirable to establish and maintain oscillations of the sample about its equilibrium position. A technique which enabled rapid damping of sample oscillations, or which forced the sample to oscillate and maintained the sample in oscillation would be of considerable value.
It is often necessary to determine the force which an acoustic field can exert on an object for a predetermined displacement of the object from an equilibrium position. For example, this enables an operator to determine whether the acoustic energy is of sufficient intensity to prevent the object from reaching the walls of the chamber under a given gravity or microgravity equilivent. While it is possible to place an object at the end of a thin wire or rod and measure the force on the object for a given displacement from an equilibrium position, this technique does not accurately indicate the forces on the object under conditions such as large heating of the object to melt it and the consequent uneven heating of the gas within the chamber, especially if the chamber dimensions are altered to produce movement of the object. A simple method for determining the relative force on the object for a given displacement from its equilibrium position would be of considerable value.